As a prior vertical indicator unit, it has been known "a measuring pole comprising an exterior pipe, an interior pipe pole connected to the inner lower portion of the exterior pipe by freely rotatable ball joint coupling, and a liquid filled in an allowance portion between the exterior pipe and the interior pipe pole, so as to secure completely verticality of the interior pipe pole" (Japanese Patent Application Laid Open No. 60-131,420) (See FIG. 5.)
This measuring pole fills a liquid between the exterior pipe and the interior pipe pole, but does not hermetically seal the open end thereof, so that there is such a disadvantage that the pole cannot be laid horizontally for housing.
As shown in Japanese Patent Application Laid Open No. 61-274,639, it has also been known "a vertical indicating float comprising a vessel containing a liquid therein, and a base-open type float vessel connected to the lower end of pole portion of the liquid-containing vessel by vertical supporting rod with allowance for the inner wall of said pole portion, thereby lowering an atmospheric pressure of an upper chamber of the vessel and raising an atmospheric pressure of an inner chamber of the said float vessel, so as to produce buoyance in an imaginary space including apparatuses in the float vessel" (ref. FIG. 6).
In this float, a liquid is filled in an upper vessel of a supporting frame, a bottom-open type float vessel inserted into said upper vessel is floated on the liquid of upper vessel of the supporting frame, the bottom-open type float vessel is connected to an inner lower end portion of the supporting frame by a vertical supporting rod and connecting rod or cord, the liquid is filled up to the imaginary water surface, the supporting frame is hermetically sealed by sealing plug means, and a gas is filled in an upper chamber of the supporting frame with pressure from the sealing plug means, thereby generating a differential level on the water surface in the float vessel and the water surface in the vessel of the frame, and standing the supporting frame for attracting the float within allowance, so as to obtain a vertical indicating line in the connecting rod or cord connected between float and the lower end of supporting frame.
This float type vertical indicating pole unit has a shortcoming that it takes much time for obtaining a vertical indicating line, and if a supporting frame is laid horizontally, an open upper end of the pole portion of supporting frame warps or make errors in a vertical supporting mechanism by the movement of liquid from the upper vessel to float vessel or the pole portion of the supporting frame, thereby liquid filling and gas filling with pressure should be started again.
The prior vertical measuring pole by means of a float was inconvenient by housing an indicating portion within a vertical indicating pole portion of the frame vessel for hermetically sealing a liquid.